In a motor vehicle, a fuel for an internal combustion engine can be conveyed or pumped by means of a high-pressure injection system. A high-pressure injection system of this kind has a high-pressure pump which can convey the fuel toward the internal combustion engine on a high-pressure side with a pressure of greater than 200 bar. The fuel pump can have a piston which is moved back and forth between a bottom dead center and a top dead center in a compression chamber or swept volume. To this end, the piston can be driven, for example, by a motor shaft of the internal combustion engine. A complete cyclical movement of the piston is referred to as the pump cycle here.
As part of the piston movement from the top dead center to the bottom dead center, an opening movement of an inlet valve of the high-pressure pump begins, in each pump cycle, starting from a specific opening position of the piston. This is then the beginning of an intake phase in which fuel or, in general, a fluid flows into the compression chamber through the inlet valve. After the bottom dead center is reached, the intake phase ends and the piston is moved back toward the top dead center. During this expulsion phase, the fluid is expelled from the compression chamber again by the movement of the piston toward the top dead center. Provided that the inlet valve is open in this case, the fluid flows back to a low-pressure side through the inlet valve. Therefore, the inlet valve is closed by a control device by current being applied to an electromagnet during the movement of the piston toward the top dead center. The electromagnet to which current is applied magnetically attracts an armature which is connected to the inlet valve, so that said valve is carried along. When the inlet valve is closed, the fluid is no longer expelled through the inlet valve, but rather through an outlet valve, owing to the piston movement. The outlet valve may be, for example, a non-return valve. The fluid which is expelled through the outlet valve generates the fluid pressure on the high-pressure side downstream of the outlet valve.
The described opening movement of the inlet valve from the closed position to the open position creates the problem that the inlet valve stops when it reaches the (completely) open position and as a result generates undesired noise. In order to counter this generation of noise, a restraining current can flow through or be applied to the electromagnet during the opening movement in order to brake the opening movement by way of the magnetic force generated as a result, so that the inlet valve stops more gently or at a lower speed in the opening position.
Since the inlet valve moves away from the electromagnet during the opening movement, the restraining current of said electromagnet is continuously increased in order to exert a constant braking force on the inlet valve. The critical factor here is the starting current which has to flow while the inlet valve is released from the closed position. Here, this starting current is called the initial attenuation current, or attenuation current for short. If the current intensity of the attenuation current is too high, an excessively high restraining force is exerted on the inlet valve by the electromagnet, as a result of which it does not open at all or opens too late, this in turn having an adverse effect on the intake phase and therefore the efficiency of the high-pressure pump. If the attenuation current is too weak, the inlet valve can be released from the closed position with too much momentum or with too much acceleration, so that the restraining current which then flows no longer provides sufficient braking for effectively attenuating the noise.